It is not uncommon to encounter rusting and unclear labeling of nameplates during transformer testing, especially for old equipment with long operating years. At this point, if you guess the wiring according to an unknown connection method, the measured group will either report an error or not match at all. The blind testing function of HZTTR80A is specifically designed for this situation.

What is blind testing logic

In normal mode, the operator needs to inform the instrument in advance whether the high voltage side is connected in Y or D, what connection method is used on the low voltage side, and what the group number is. The instrument verifies whether the measured results are consistent based on this. In blind measurement mode, the high voltage connection and low voltage connection are both selected as "unknown". The instrument calculates the actual connection method and group number by measuring the amplitude and phase relationship of the three-phase voltage, and the operator does not need to have any wiring information in advance.

operating steps

Enter the parameter settings interface, select "Unknown Connection Method" for both "High Voltage Connection" and "Low Voltage Connection", and also select "Unknown Group Number". Then connect the wires normally for measurement. After the instrument completes the measurement, the result interface will display two key contents:

① The vector relationship diagram of the primary and secondary side voltages visually displays the actual phase difference between the voltages on both sides; 

② List of possible connection groups for reference and judgment by operators.

By clicking the "Help" button on the results interface, you can also access the built-in IEC 60076-1 standard commonly used three-phase transformer connection vector group reference diagram. The left side is the standard vector group, and the right side is the vector diagram of the current measurement result. Comparing the two, there is basically no need to rely on experience to guess, and it can be seen at a glance which group it corresponds to.

It can also be known on one side and tested blindly on the other side

If it is known that the high voltage side is connected to YN, but the low voltage side connection method is uncertain, YN can be selected for the high voltage side and "unknown" for the low voltage side. The instrument will narrow down the judgment range based on the known connection on one side, resulting in more accurate results.

Precautions during use

The wiring method for blind testing mode is exactly the same as that for normal mode, without any additional operations. However, it should be noted that for Y/yn, YN/d, D/yn, D/zn, Y/zn, and autotransformers, there is no need to connect the neutral point N; only for single-phase transformers and PT testing, a pair of yellow and black test clips on the high and low voltage sides should be used, and the rest of the wires should be suspended. Blind testing also follows this rule, and unknown connection methods do not mean arbitrary wiring.